This animation made of images from the microscopic imager instrument on the Mars Exploration Rover Spirit shows the patch of soil scientists examined at Gusev Crater just after Spirit rolled off the Columbia Memorial Station. The upper left corner of the soil patch in part of this animation is illuminated by direct sunlight and thus appears brighter. The actual size of the patch is about 3 centimeters (1.2 inches) across. Scientists initially thought that the soil was dust-like and therefore would collapse as the instrument pressed down on it with approximately 4 ounces (113 grams) of force. But they were surprised when, as the rotating frames show, the soil barely moved under the instrument's weight. Scientists are still determining why this happened.